Conventionally, electron beam drawing apparatuses and the like for performing electron beam lithography have been developed. See, for example, JP 2013-503486A (Tokuhyo) and JP 2012-501476A (Tokuhyo).
Photomasks are used in lithography processes in the manufacture of semiconductors. As the fineness of photomasks recently increases, modification of patterns and addition of auxiliary patterns are often performed using resolution enhancement technique (RET) such as optical proximity correction (OPC). A mask pattern produced by inverse lithography (ILT) which is a type of RET is configured by curved lines.
Currently, photomasks are produced by a drawing machine using electron beams according to the variable shaped beam (VSB) method. However, drawing with electron beams according to the VSB method is applicable only to rectangles with variable size. Thus, a curved line portion is drawn using approximation. According to conventional methods, after a curved line is divided into trapezoids, each trapezoid is approximated into a rectangle. Accordingly, the number of rectangles increases, and the mask drawing time becomes long.